Synthesis Of Ordered Mesoporous Carbon/ge Composite Electrode Materials And Their Lithium/Sodium Storage Properties

The depletion of fossil fuels and the construction of ecological environment require that the driving energy of vehicles should convert from traditional fossil oil to green renewable energy,which put forwards higher requirements on the energy storage devices.Advanced material technology is an important basis of energy storage industries.Therefore,the research of new anode materials for lithium/sodium-ion batteries with higher specific capacity and energy density has attracted widespread attention in recent years.Among them,germanium element in group IV has been recognized as a promising anode material for secondary battery systems owing to its high theoretical capacity.However,the electrochemical performance of Ge electrode could be hindered due to the huge volume expansion and structural damage of the Ge crystals during charge-discharge process.In this dissertation,we used heteroatom-doped mesoporous carbons(N and S co-doped ordered mesoporous carbons),two-dimensional ordered mesoporous carbons(CMK-3)and three-dimensional ordered mesoporous carbons(CMK-8)as conductive skeleton and matrix to disperse Ge nanoparticles,respectively.A series of ordered mesoporous carbon/germanium composites were designed and synthesized to buffer mechanical stress caused by volume expansion of Ge crystals during charge-discharge process,so as to achieve higher electrochemical performance of Ge electrode in LIBs or SIBs.The main contents can be summarized as follows:Firstly,the nitrogen and sulfur co-doped ordered mesoporous carbons(OMC-N-S)were obtained through heteroatom co-doping modification,then OMC-N-S/Ge composite was further synthesized by nano-casting combined with calcination method.When applied as an anode material for LIBs,it displayed superior reversible capacity(1200 mAh g-1 at 0.1 A g-1 after 200 cycles)and excellent long-term cycling stability(650 mAh g-1 at 2 A g-1 even 1000 cycles).The results show that the co-doping of N and S,OMC,and Ge play a synergistic role in storing lithium,which endowed OMC-N-S/Ge electrode with high specific capacity,excellent rate performance and long-term cycle stability.Secondly,the two-dimensional ordered mesoporous carbons(CMK-3)was synthesized and used as a nano-reactor to load Ge nanoparticles.Subsequently,in order to decorate the part of Ge nanoparticles that exposed outside the CMK-3 channel,the chemical vapor deposition treatment was introduced to fabricate CMK-3/Ge-C composite with different CVD treatment times(30 and 60 min).The results show that an amorphous carbon coating on the surface of annealed CMK-3/Ge is beneficial to sodium storage,especially for the CMK-3/Ge-C composite with 60 min CVD coating.When used as an anode material for SIBs,it exhibited an excellent rate performance and long-term cycle stability.Finally,the three-dimensional bicontinuous mesochannel of CMK-8 was synthesized and selected as a confined host to prepare CMK-8/Ge nanohybrid,which showed up excellent electrochemical properties for lithium and sodium storage.The outstanding performance of the CMK-8/Ge composite is attributed to its unique three-dimensional structure and interpenetrating tunnels,including homogeneous particle distribution of Ge nanoparticles,and highly conductive CMK-8 carbon matrix,which facilitate electron and ion transportation and guarantee electrolyte accessibility.